1. Field of the Invention
This invention relates generally to metal ion plating and metalizing and more particularly to a metalizing or ion plating process utilizing a vacuum chamber filled with an inert gas and a combination of RF power and positive DC voltage applied to a substrate to be plated and a combination of RF power and negative DC voltage applied to the ion source in the inert gas under vacuum to optimize the deposition of metal plating materials and dielectric materials.
2. Brief Description of the Prior Art
A process known as "sputtering" is known in the art wherein a starting material (material to be deposited), usually a metal, is arranged within an evacuated chamber in spaced relation to a receiving substrate (the object to be coated). Typically, the substrate is arranged on a grounded electrode, and the chamber is back-filled with a gas at low pressure. The material to be deposited is positioned on a conductive electrode to which a source of potential is applied. The potential source serves both to produce a gas plasma between the spaced electrodes, and to cause gas ions from the plasma to bombard the surface of the starting material (material to be deposited). Such ion bombardment acts to break or knock off atoms or molecules of the starting material, causing them to fly ion all directions. Some of these atoms or molecules of the starting material settle on the substrate and form a layer.
In the process known as "ion plating", a conductive starting material (material to be deposited), usually a metal, is placed within an evacuated chamber in spaced relation to a conductive receiving substrate (the object to be coated). A high voltage DC field is produced between the starting material and the substrate, and the chamber is then back-filled with a gas to a pressure to generate and sustain a plasma discharge. The starting material is then vaporized to form a vapor deposit of the starting material on the substrate. In the presence of the plasma, a portion of the vaporized starting material becomes ionized, and the positively charged evaporant ions and positively charged gas ions are accelerated by the electric field and bombard the substrate surface to densify the vapor deposited coating.
White, U.S. Pat. No. Re. 30,401 (reissue of U.S. Pat. No. 4,039,416), discloses a gasless ion plating process wherein plating material is melted, vaporized and then subjected to an ionization environment in a low pressure chamber with a "virtual cathode" consisting of a plasma of ionized atoms of evaporant material created by evaporating in an RF field. White teaches applying a positive DC voltage to the evaporative metal and applying a negative voltage to the object to be plated. When the plasma is generated it flows everywhere in the tank and when the DC source is applied, it has the effect of stopping plasma around the object to be plated. Very little plating action takes place out of the line-of-sight.
White, U.S. Pat. No. 4,420,386 discloses a method for ion plating using magnetic fields wherein plating material is vaporized and subjected to an ionization environment in a low pressure chamber. An electron saturated magnetic field is placed adjacent the substrate for positive ionization of the evaporant atoms of the vaporized plating material. A negative bias is applied to the substrate for attracting positive ions of the vaporized plating material.
White et al, U.S. Pat. No. 4,342,631 discloses a gasless ion plating process and apparatus which eliminates the need for electrically isolating the substrate from the evacuated chamber. A positive DC bias is developed on the plating source relative to the substrates by applying a DC positive voltage to the plating source to create an electrical field between the source and substrates for accelerating the plating ions towards the substrates for plating the same.
Weiss et al, U.S. Pat. No. 4,170,662 discloses a plasma plating method for forming a dense layer of non-conductive material on a substrate wherein the starting material is vapor deposited on the substrate while simultaneously bombarding the substrate with ions of a gas. An RF field is established between the substrate and an opposing electrode structure to produce a plasma of the gas in the vicinity of the substrate. A negative bias is created in the electrode connected to the substrate to render the electrode attractive to the positively charge ions in the plasma.
Cuomo et al, U.S. Pat. No. 4,250,009 discloses a particle beam deposition system wherein an energetic particle beam is accelerated toward a starting material located at an angle relative to the path of the beam to form both positive and negative ions. The voltage difference between the target and substrate can be adjusted to be positive or negative so that either positive or negative ions can be accelerated to the substrate.
Mattox, U.S. Pat. No. 3,329,601 discloses a method and apparatus for coating a substrate from plasma of ionized coating material wherein the starting material is connected to a filament within an evacuated chamber in spaced relation to a receiving substrate, and a high voltage DC field (generally 1000 volts or more) is produced between the starting material and the substrate, and the chamber is filled with a gas to a pressure to generate and sustain a plasma discharge. The starting material is then vaporized to form a vapor deposit of the starting material on the substrate. The substrate is connected to the negative terminal of the high voltage DC source and the filament and starting material to be vaporized is connected to the positive terminal of the high voltage DC source.
The present invention is distinguished over the prior art in general, and these patents in particular by the present process wherein the substrate to be plated is suspended in a vacuum chamber filled with an inert gas and radio frequency is supplied to the substrate to be plated to create a plasma which is maintained by the inert gas. Positive DC voltage is then applied to the substrate and negative DC voltage to the filament. Power is then applied to the filament, and upon vaporization of the ion source a plasma of evaporated and ionized deposition material is created between the ion source and the substrate to optimize the deposition of metal plating materials and dielectric materials. The ion source, or vaporizing material is wrapped around a filament which is enclosed within the vacuum chamber. One side of the filament is connected to ground and the vacuum chamber is also grounded. The RF power supply feeding power to the substrate is connected to ground and to one side of the wrapped filament and ion source. The DC voltage supply has its positive terminal connected to the RF power line feeding the substrate and its negative terminal joined to the RF power line which is connected to one side of the filament and grounded. Wire mesh grids may be placed between the high temperature ion source and the substrate for more complete control of the plasma, and to direct the plasma flow to certain locations on or around the substrate to be plated. A voltage source may be connected to the grid to control plating on certain parts of the substrate.